Attenuator



. Dec. 20, 1949 c. P. CARLSON ATTENUATOR 2 Sheets-Sheet 2 Filed Aug. 24,1945 FIG. 7

s: a. E= iii; O

//v l/ENTOR C. P CARLSON ATTORNEY Patented Dec. 20, 1949 UNITED STATESPATENT OFFICE 2,491,644 Arr-environ -Carl P, Carlson, Tenafly, J.,assignor tdBell Telephone Laboratories, Incorporated, New

York, N. Y., a corporation of New York Application'August z l, 1945;Serial No. 612394 'liClai'ms. (c1. its-44) This invention relates toattenuators and more particularly to variable attenuators for use withwave guides.

The principal object of the-invention is to attenuate electromagneticenergy flowing in ahollow wave guide. Other objects are'to make theattenuation in decibels of a variable wave guide attenuatorsubstantially proportional to the angular rotation of a resistiveelementand to increase the maximum attenuation obtainable.

The variable wave guideattenuator in accordance with the presentinvention comp-rises a straight,- hollow Wave guide having alongitudinal slot ina wall thereof and arotatable resistive vanemounted-so that its edge projects through the slotinto the guide. Thecontour of the vane deviates from thearc of a circle in such away thatthe attenuation-indecibels is substantially proportional to the anglethrough which the vane is rotated. In this way,- congested regions inthe attenuation scale are avoided, permitting-a more accurate-settingofthe attenuator. To increase the maximum attenuation obtainable thevane may cut clear throughthe'guide and emerge through a second slot inthe wall.

The nature of the invention will bemore fully understood from thefollowing detailed-description and by reference-to the accompanyingdrawing, in which like reference characters refer to similar orcorresponding parts and in which;

attenuator in accordance with the invention;

Fig. 2 is a side view thereof;

3 shows a transverse cross-section taken on the line 3-3 of Fig. 2;

Fig. 4 shows a partial longitudinal cross-section taken on the line 4-4of Fig. 1;

Fig. 5 is a side view of another attenuator in accordance with theinvention, employing only a single slot;

Fig. 6 is an end view of the attenuator of Fig. 5;

Fig. 7 shows a transverse cross-section taken on the line l-l of Fig. 5;and

Fig. 8 is a longitudinal cross-section taken on the line 8-8 of Fig. 6.

The variable wave guide attenuator shown in Figs. 1, 2, 3 and 4comprises a hollow, straight wave guide In having two oppositelydisposed slots II and [2 in the opposite sides l3 and M, respectively,and a resistive vane l6 rotatably mounted about the pivot point i5 sothat its edge will enter the guide 10 through the upper slot l l andemerge through the lower slot l2. The vane I G is preferably positionedparallel to the transverse electric field of itheelectromagnetic wavesto be attenuated. In the guide It, which is of rectangular cross-sectionwith'unequal cross-sectional dimensions; this field is ordinarilyparallel to the nar rower sides 11 and 18, as indicatedby the arrowEin'Figs; 2, 3 and 4. The slo'ts H and I2 are, therefore; in the widersides l3 and Hand are preferably centrally located so that the vane 116will be in the most intense portion of the field.

The vane I6 is clampedbetween the two blocks l9 and 20 by the'bolts 22and secured to the shaft 23by the pins 24. The'shaft 23, which has ahead 21, turns in bearings in tl'ie two upright supports 25, secured tothe sides H and 18 0f the guide It. The edge of the vane 16 is' centeredin the slots H and ;l2 by means of the spacers 26. A knob 28 attached tothe shaft 23 by a set screw 29 facilitates turning. A dial 30 attachedto the lmqb 2. a a stale +7 ca r te 'ied i ni which the attenuationintroduced may be read at the index 32. A spring washer}; between the det! a d e supp rt}? t k upefid a r the shaft 23. V The end flanges 34are provided for connecting the guide 10 'to othersections of wave ie-..

s shown in the drawing, the'vahe it is entirely withdrawn from theinterior of the guide l0 and the attenuation reading iszero. Tointroduce attenuation, "the vane ltjis rotated in a counterclockwisedirection about the pivot point '15 by'ineanaof the kriob'28. The edgeof the vane it enters the guide Ill through theu'pper slot ll, passesall the way across the guide, and eventually comes out through the lowerslot l2 on the other side. Permitting the vane It to extend clearthrough the guide increases the maximum attenuation obtainable with theattenuator. The contour of the vane It preferably so deviates from thearc of a circle that the attenuation in decibels introduced issubstantially proportional to the angle through which the vane isrotated. Congested regions in the scale 3| are thus avoided and moreaccurate attenuation settings are possible.

Figs. 5, 6, 7 and 8 show a modified embodiment of a variable wave guideattenuator in accordance with the invention in which the guide has onlya single slot. The attenuator comprises a straight, hollow, rectangularwave guide 36 having a slot 31 centrally located in one of the widersides 38 and a resistive vane 39 mounted for rotation about the pivotpoint All so that its edge will project through the slot 3'! into theinterior of the guide 36.

The vane 39 is clamped between two circular plates 42 and 43 by means ofsix screws 44 and the assembly is secured to the inner end of the shaft45. This assembly is enclosed in a metallic shield formed of the twocircular plates 4'! and 48 and a short cylinder 49 securely attached atits base to the guide 36. The plate 48 carries a journal box 50 in whichrotates the flanged cylindrical bearing 5| surrounding a portion of theshaft 45. The edge of the vane 39 is centered in the slot 31 by thewasher 53. A knob 54 attached to the outer end of the shaft 45 by a setscrew 55 carries a dial 56 with a scale 51, calibrated in decibels ofattenuation, which may be read at the index 58. A spring washer 59between the bearing 5| and the knob 54 prevents end play in the shaft45.

As shown in Figs. 5, 6, 7 and 8 the attenuator is set at zero andtherefore the vane 39 is entirely withdrawn from the guide 35. However,

as the knob 54 is turned in a counter-clockwise A direction the edge ofthe vane 39 gradually passes through the slot 31 into the interior ofthe guide 36 and the attenuation is increased correspondingly. In thisattenuator, also, the contour of the vane 39 preferably so deviates fromthe are of a circle that the attenuation in decibels is a substantiallylinear function of the angular rotation.

What is claimed is:

1. A variable attenuator for electromagnetic waves comprising a hollowwave guide having a longitudinal slot in a wall thereof, a rotatableresistive vane mounted so that its edge projects through said slot intosaid guide, and a metallic shield enclosing said vane, the contour ofsaid vane so deviating from the arc of a circle that the attenuation indecibels is substantially proportional to the angular rotation of saidvane.

2. An attenuator in accordance with claim 1 in which said guide has asubstantially straight longitudinal axis.

3. An attenuator in accordance with claim 1 which includes a second slotin the wall of said guide, said slots being oppositely disposed and saidvane being so shaped that, upon rotation, it cuts clear through saidguide and emerges through said second slot.

4. An attenuator in accordance with claim 1 in which said vane isparallel to the transverse electric field of the electromagnetic wavesto be attenuated.

5. An attenuator in accordance with claim 1 it which said guide is ofrectangular cross-sectior and said slot is centrally located in one ofthc sides thereof.

6. An attenuator in accordance with claim 1 in which said guide is ofrectangular cross-section with unequal cross-sectional dimensions andsaid slot is in one of the wider sides thereof.

7. An attenuator in accordance with claim 1 in which said guide is ofrectangular cross-section with unequal cross-sectional dimensions andsaid slot is centrally located in one of the wider sides thereof.

8. A variable attenuator for electromagnetic waves comprising a hollowwave guide having two oppositely disposed longitudinal slots in the wallthereof and a rotatable resistive vane mounted so that, upon rotation,its edge enters said guide through one of said slots and emergestherefrom through the other of said slots.

9. An attenuator in accordance with claim 8 in which the contour of saidvane'is so shaped that the attenuation in decibels is substantiallyproportional to the angular rotation of said vane.

10. An attenuator in accordance with claim 8 in which said vane isparallel to the transverse electric field of the electromagnetic wavesto be attenuated.

11. An attenuator in accordance with claim 8 in which said guide is ofrectangular cross-section and said slots are centrally located inopposite sides thereof.

12. An attenuator in accordance with claim 8 in which said guide is ofrectangular cross-section with unequal cross-sectional dimensions andsaid slots are in the wider sides thereof.

13. An attenuator in accordance with claim 8 in which said guide is ofrectangular cross-section with unequal cross-sectional dimensions andsaid slots are centrally located in the wider sides thereof.

CARL P. CARLSON.

REFERENCES CITED UNITED STATES PATENTS Name Date Schelkunofi Mar. 21,1939 Number

